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America's Stone Age Explorers

Classroom Activity

Materials | Procedure | Activity Answer | Links & Books | Standards  Print this Teacher's Guide (PDF, 4 pages)

Objective
To learn how mitochondrial DNA (mtDNA) is inherited.

• copy of the "The Hunt for mtDNA" student handout (PDF or HTML)

1. Because mtDNA is only passed down along maternal lines and mutates at predictable rates, it has been used to help trace migration routes of early humans. In this activity, students will learn how mtDNA gets passed along maternal lines.

2. To set up the activity, tell students that they will be working as forensic scientists to help solve a long-standing "missing persons" case. Provide each team with a copy of "The Hunt for mtDNA" student handout. Explain to students what mtDNA is, how it differs from nuclear DNA, and how it is inherited (see Activity Answer for more information).

3. Set up the challenge: An anthropologist has found a few human bones at a site in South Africa. Investigators think they might belong to a Nobel Prize-winning dung beetle biologist who disappeared in Africa. Since the bones have been exposed to severe weather for many years, the only DNA that may be salvageable is mtDNA. Investigators have compiled a pedigree chart that lists all the missing person's relatives. But investigators are having problems identifying his maternal relatives. Which of the people in the "Who's Related by mtDNA?" pedigree chart carry the great-great grandmother's mtDNA, and of those people, which living relatives would be eligible to donate their mtDNA for comparison? (Mitochondrial DNA can be retrieved from exhumed remains, but this is a costly process and can be emotionally difficult for families. When possible, it is always best to retrieve mtDNA from a living relative. Mitochondrial DNA cannot be retrieved from cremated remains.) The missing person is labeled with a question mark in the pedigree chart.

4. After students have completed the challenge, discuss their results. What do students conclude about the inheritance patterns of mtDNA? Why aren't the dung beetle biologist's children eligible for testing? How far back can mtDNA of an individual be traced?

5. As an extension, have students research how mtDNA has been used to trace migratory routes of early humans.

Everyone carries two types of DNA: nuclear DNA, found in the nucleus of each body cell, and mitochondrial DNA (mtDNA), found in the mitochondria located in the cell's cytoplasm outside the nucleus. Nuclear DNA codes for most proteins made by the cell and is responsible for the inheritance of physical traits, such as hair color or whether a person has dimples, as well as inherited genetic disorders, such as sickle cell anemia or Tay-Sachs disease. Mitochondrial DNA codes for its own proteins and for ribosomal and transfer RNAs.

During reproduction, the father's sperm cell—which contains both nuclear DNA and mtDNA—donates only its nuclear DNA to the zygote that results from the fusion of the sperm with an egg cell. (Some researchers argue that a fragment of the father's mtDNA is in fact passed on, though it represents much less than 1 percent of the total.) Therefore, all the DNA in a person's mitochondria comes from his or her mother. This means that each new generation has only the mtDNA of the mother, who has only the mtDNA of her mother, and so on. (Males have only the mtDNA of their mothers as well but do not pass it on.) As a result, mtDNA samples can be used to identify any maternally related individuals.

The people related to the missing person's maternal grandmother (who are the candidates for getting mtDNA to compare to that of the missing person), are connected with heavy lines in the pedigree chart below. The 10 living relatives eligible for testing are shaded.

Who's Related by mtDNA?

Mitochondrial DNA could be used to confirm that two brothers with the same mother who died in a crash were related, but not to distinguish the brothers' remains from each other in the way that nuclear DNA could. In theory, mtDNA could be traced back to the first "mitochondrial Eve," a woman whom scientists have tried to pinpoint. However, controversy exists regarding the usefulness and accuracy of molecular clocks used to date when a mitochondrial Eve might have lived. (Molecular clocks are based on assumptions about how regularly DNA mutations occur.)

Web Sites

NOVA Web Site—America's Stone Age Explorers
www.pbs.org/nova/stoneage/
In this companion Web site to the program, consider who or what killed off the mammoths and other megafauna 13,000 years ago, view a gallery of images of Clovis artifacts, peruse an Ice Age North American map to learn more about pre-Clovis sites, and match Stone Age artifacts to their uses.

Center for the Study of the First Americans
www.centerfirstamericans.com/cat.html?c=4
Contains articles on theories regarding the peopling of North America.

Clovis and Beyond
www.clovisandbeyond.org/
Includes articles on possible coastal migration routes and the Solutrean-Clovis link.

Book

Adovasio, Jim and Jake Page. The First Americans: In Pursuit of Archaeology's Greatest Mystery. New York: Random House, 2002.
Challenges the theory that the Clovis people were the earliest settlers of the Americas.

Dixon, James E. Bones, Boats, and Bison. Albuquerque: University of New Mexico Press, 1999.
Argues that the earliest humans in North America were not big-game hunters following mammoths across the Bering Land Bridge but rather general foragers colonizing the New World.

Tankersley, Kenneth. In Search of Ice Age Americans. Salt Lake City: Gibbs Smith, 2002.
Draws on fieldwork worldwide to try to reconstruct the daily lives of the earliest Americans.

The "Hunt for mtDNA" activity aligns with the following National Science Education Standards:

Grades 5-8

	Science Standard C: Life Science

Reproduction and heredity:

• Reproduction is a characteristic of all living systems; because no individual organism lives forever, reproduction is essential to the continuation of every species. Some organisms reproduce asexually. Other organisms reproduce sexually.

Grades 9-12

	Science Standard C: Life Science

The molecular basis of heredity

• In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular "letters") and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosome.

Classroom Activity Author

This classroom activity originally appeared in a slightly different form in the companion Teacher's Guide for NOVA's "Last Flight of Bomber 31" program.